In the market, there is a high demand for plastic materials not only complying with structural and processability requirements which are characteristic of polymers as raw materials, but also to be able to solve further specific and engineering problems. In this context, during the last years a great demand for plastic materials having the property of inhibiting adherence of microorganisms (antifouling) or being antimicrobial has been generated, in such a manner that they can be used in applications so varied such as materials subjected to water flows inhibiting adherence of algae or microorganisms, as well as on fabric or air filters surfaces which require controlling the growth of microorganisms on those surfaces. The latter is more relevant if thermoplastic polymers are addressed, in particular those based on polyolefins (polyethylene or polypropylene), since those represent over 50% of current plastic market, as well as other thermoplastics.
The present invention describes a technology which allows to incorporate structures based on nanoparticles of an element or inorganic compound of specific characteristics, in particular biocidal, to a resin of a thermoplastic and/or thermostable polymer, also to organic coatings such as paintings, resulting in a plastic material which can release ions of said element or inorganic compound in a controlled manner, at a high release rate during the first periods of time, and also maintaining said release rate for long periods of time, maintaining the main features of the resin. This ability to release ions of the new material results in a biocidal plastic, i.e., antimicrobial and/or antiadherent (Antifouling), highly bioactive and long lasting. Thanks to the property of the material of the present invention regarding the high release rate in short times (First days), and due to the control in the release of ions in long term, and also the control of dispersion of the inorganic compound in the polymeric resin, this product overcomes the limitations of other equivalent technologies currently available (metallic alloys based in copper and/or paintings with copper), in particular those related with environmental and processing impact.
The present invention can be used with any polymeric organic resin, as previously described, but thermoplastics are preferred, and in particular polyolefins (polyethylene and polypropylene), wherein the latter represent more than 50% of all commodity plastics, being the most consumed plastic materials currently. Nevertheless, plastic resins are inert to microorganisms, which allows that certain applications during its performance are reduced due to microorganism accumulation, limiting its lifetime, or that in certain applications said resins do not help to avoid propagation of diseases associated to microorganisms. The present invention solves this limitation by incorporating a biocidal or antifouling property to the resin, in order to control distribution and aggregation of the incorporated filling. Current solutions for this problem are adding a compound that can release an agent in time to a resin or changing the plastic material for a copper alloy, of a much higher cost and quite difficult to process. Most of these solutions present a disadvantage, which is the inability to control the release rate of the agent (specially at short times during the first days) and/or biocidal properties of the material are maintained for only a short time, and also, there is no disclosure regarding a dispersion control in the filling, that is to say, the biocidal agent in the polymeric resin, which decreases the bioactive potential of the resulting material. The present invention allows to produce a thermoplastic and/or thermostable material, besides other organic coating, such as painting type, with a controlled antifouling or biocidal property, which depends on the fabrication method, and of prolonged activity, which is a relevant improvement over other existing solutions such as the case of plastic nets covered with copper based paintings and/or the direct use of metallic nets, which for example in aquaculture industry, as well as other applications as those related to intrahospital infections. These advantages are related to a higher flexibility of the material, better processability, reduction in maintenance processes, less weight and ease of operation. Furthermore, when releasing the biocidal agent at a high rate during initial periods of use (first 10 days), and thanks to the dispersion control of the filling or biocidal agent in the polymeric resin, the material avoids the growth of microorganisms in a more effective way than other solutions. To this is added the improvement of environment since the controlled release of the ion of the element or inorganic biocidal compound. The material of the present invention is elaborated by incorporating particles of a biocidal element or inorganic compound into a resin, in a particular case polypropylene, generating a plastic material which can release in a controlled manner ions of the biocidal element or inorganic compound during long periods of time, maintaining its main properties of processability thanks to the dispersion of the biocidal agent in the polymeric resin. That is to say, the resulting material still is a plastic but the technology applied allows to control the kinetics of ion release in time, which is given by the amount and distribution of the active agent, which generates a flexible material that can be produced according to specific needs for its use. In particular, release of the active agent depends directly on its concentration in the resin, and as example, release rates of 5 μg/ml after 100 days in a concentration of 10% w/w are obtained, which can be doubled if the concentration is increased to 50% w/w. The control of dispersion of the filling or biocidal agent is other feature that allows controlling the release of ions, and in this way, the release of the active agent can be improved in more than 40% by only improving the dispersion of particles by using a pre-treatment. This is a huge advantage compared to other existing alternatives, for its flexibility, allowing to comply with potential toxicity norms and processability. Furthermore, by initially releasing ions at a high rate, this material would effectively avoid proliferation of microorganisms during its first initial adhesion stage to the surface thereof.
This new material can be used in all applications where avoiding adherence or growth of microorganisms is needed, such as in aquaculture industry, hospital establishment surfaces, gutter drains, food processing industry, up to common daily massive use articles, such as cell phone housings, door handles, and in general, any surface which is required to maintain a suitable control of microorganism growth.
Thus, this material has a broad market and is worth noting that in Chile, only in 2007 nearly 400 thousand metric tons of polyolefins were processed, from a total of 700 thousand metric tons of plastics. Of many of potential applications of this new product (for example, aquaculture apparatuses, hospital, food industry, packing, etc), the material of the invention is particularly suitable for fabrication of antifouling nets, such as for example in the use of aquaculture, as well as in the fabrication of plastic materials to be used in hospitals, clinics or other applications where the growth and presence of microorganisms is to be controlled. Using as an example the development of salmon industry in Chile, the second worldwide salmon producer, and with no intention of limiting the scope of the present invention, whose uses are very broad, as previously noted, the potential use of the material of the present invention will be explained. In particular, and only as a way of exemplifying one of the many applications that the polymer with biocidal, antifouling activity, of the present invention, and with no intention of limiting the scope of the invention to this particular application, the use of the resin (polymer with biocidal activity) will be described in the fabrication of a net for salmon farming, using a antimicrobial plastic avoiding the fouling phenomena.
Chile has approximately 4 thousand cage systems for aquaculture. It has been reported that one of the most relevant problems of these systems is due to the presence of biological fouling, generating over 45 million US dollar increase in costs yearly. Thus, the use of the material of the present invention limits this issue, producing a direct increase in profit of salmon industry. Also, it is known that worldwide, aquaculture is growing between 7% and 8% yearly. Along with this, and in particular in the case of Chilean salmon industry, which only has 196 operative farming centers of a total of 400, thus Chile has a potential margin of even higher growth, since it already has suitable installations. Again, it is emphasized that the example of salmon industry is only provided as an exemplification of one of many applications that the material of the present invention can have, therefore, the present invention also encompasses other applications wherein the antimicrobial polyolefins, or thermoplastics in general, would have high demand generating a direct benefit to those firms, product of this technology. One of the advantages of the present invention is the control of release of ions, making the material a highly flexible design material, which allows complying with specific requirements and different environmental norms. This is a clear advantage over copper nets or paintings including copper currently available for the salmon industry, besides being economical.